Fluid flow direction indicator



July`18, 1950 G. E. MORRIS FLUID FLOW DIRECT l ON INDI CATOR July 18, 1950 G. E. MORRIS 2,515,251

FLUID FLOW DIRECTION INDICATOR Filed June 50, 1948 2 Sheets-Sheet 2 Patented July 18, 1950 UNITED STATES PATENT OFFICE (Granted under the act of March'v 3, 1883, as amended April 30, 1928; 370 0. G. 757) n 8 Claims.

The invention described herein may be manufactured and used by or for the Goverment for governmental purposes without payment to me.

of any royalty thereon.

' This invention relates to pitch and yaw indicators and more particularly to the uid iiow null type that provides continuous angular indications of pitch and yaw with respect to the air stream.

Fluid ow direction indicators have many uses, the most extensive use probably being for aircraft. Heretofore, the pitch indicator and the yaw indicator each constituted separate and individual instruments, or, where one instrument was used, a rather complicated switching mechanism was used to adapt the device for either pitch or yaw indications. These devices which provided alternative pitch or yaw indications had the disadvantage of not providing both pitch and yaw indications simultaneously which often times is a necessity in the navigation and piloting of mobile vehicles and particularly of aircraft.

The present invention provides a single instrument ywhich gives indications of pitch and yaw continuously and simultaneously. To accomplish this, a pressure responsive device is subjected to the air stream that is responsive to pressure sense in both the vertical and horizontal planes with respect to the carrying vehicle to actuate pitch and yaw indicators simultaneously with mechanisms to maintain the differential pressures in the pressure responsive device in the null condition. The preferred arrangement in carrying out this means of indication is in the use of a hollow sensing head that is universally mounted on a support member that is adapted to be attached to a vehicle of use, as an aircraft, such that the sensing head can be rotated for a limited distance about either of two axes oriented normal to each other. Two pairs of air pick-off ports are arranged concentrically about an axis of symmetry through the sensing head that is normal to the two above mentioned axes, each pair of ports being in communication with a differential pressure responsive diaphragm switch. One pair of ports and related switch are responsive to the air stream for angles of pitch; while the other pair of ports and related switch are responsive to the air stream for the angles of yaw. 'Ihe pitch and yaw differential diaphragm switches are each in a circuit associated with a control motor that Operates to maintain the corresponding pair of pitch or yaw air ports in equal pressure relation and any rotation of the sensing head from a predetermined basic position is indicated through a self-synchronous motor-receiver coupling to indicators desirably placed. In this manner, the predetermined basic position can be fixed with respect to the vehicle carrying the device wherein relative angles of pitch and yaw with respect to the air stream may be registered.

It is a primary object of this invention to provide a fluid ow responsive indicating device for continuously and simultaneously registering angles of pitch and yaw with respect to the air stream upon being moved through the atmosphere.

It is another object of this invention to provide a single diierential pressure null position sensing device having a hollow sensing head uni .versally 'mounted on a support by two members within the sensing head each being journaled to the sensing head on an axis normal to each other and to an axis of symmetry of the sensing head, one member being rotatively held to the support by a driving element of the other member, and a driving element to rotate the one member such that actuation Of the driving elements produces a cone of rotation of the sensing head axis of symmetry with respect to its support.

It is a further Object of this invention to provide a pitch and yaw sensing device having a head member controllable in each of two normally arranged axes that are positioned substantially transversely to a longitudinal center line of the device with two pairs of pressure ports in the sensing head member arranged in two planes corresponding to the two axes that transmit the pressure sense to corresponding pairs of differential pressure responsive switches capable of controlling power means operable to maintain the head member in position about both axes to establish substantially equal pressure in the respective pressure ports.

Still another object of this invention is to provide a device to continuously and simultaneously register pitch and yaw -angulation in which a sensing head member is universally mounted on one end of a support by pivotal means on axes that are normal toeach other and swingable through arcs substantially normal to a longitudinal center line of the support by electric motor means, each motor being operative to control the head member rotation about one each of its axes in response to corresponding differential pressure responsive switches that are controlled by differential pressures impressed thereon from air ports positions in pairs in the head member symmetrically in two planes from a diametrical axis yof symmetry normal to the sensing head ro- 3 tatable axes, each pair of air ports corresponding to the differential pressure responsive switch which controls the electric motor for maintaining equal pressures in the related air ports, and self-synchronous motor-receiver means interconnecting the sensing head for each axis of rotation to position remote indicating means such that the deviation of the axis of symmetry of the sensing head with respect to the longitudinal center line of the support will be kregistered on pitch and yaw indicating means to provide a constant reference of the pitch and yaw of the device with respect to the air stream.

These and other objects will become more apparent as the description proceeds when. taken along with the accompanying drawings, in which;

Fig. l is a longitudinal Sectional View of the indicating device with parts shown diagrammatically for convenience of illustration; v

Fig. 2 shows a partial sectional view of the indicator head and support taken on the line 2-2 of Fig. 1;

Fig. 3 is an elevationalview of one setV of limit switches and related parts taken on the line 3 3 of Fig. 1 and looking in the direction of the arrows;

Fig. 4 is a schematic wiring diagram of one of the motor circuits; and

Fig. 5 is an isometric View of the sensing device as attached to an airplane wing.

Referring more particularly to Figs. 1 and 2, a tubular support I is arranged on the left end to be mounted on a front portion of a vehicle (not shown) which, for the purpose of illustration, let it be assumed to be an aircraft although the device may find uses on other types of vehicles. The forward end of the tubular support or boom IG is reduced to form a neck portion I I that ares outwardly in a mouth portion I2 `which provides a spherically contoured seat I3. Rotatably held on the seat I3 is a hollow spherical segment I4 haV- ing. an opening I into the interior at the plane I5 of the segment which opening is directed backwardly into the interior of the tubular support I0. On opposite sides of the sphere, lying on a diameter at right angles to a diameter passing centrally through the plane I6,.Which for the purpose of simplicity will hereinafter be referred to as the sphere axis of symmetry, are set screws I1 threaded through the sphere wall, the outer ends of which are recessed in a threaded bore |18 closed by caps i9 having an external spherical surface to provide an unbroken spherical surface of the spherical segment I4. The inner ends of the set screws I"I` are pointed atr 20 and the outer ends have jamb nuts 2l threaded thereon to lock the set screws I1 in position.

Within the sphere and pivoted on the set screws I1 is a semicircular member 25 having conical bearing sockets in which the pointed portions 25 of the set screws rest. The middle portion of the semicircular member 125 is divided at 21 form-` ing two connecting portions having smooth bearing surfaces 28. A bearing block 29 is positioned in the divided portion 21 and has lateral bearing extensions 30 thereon supporting hardened bearing elements 3| that are engageable with the bearing surfaces 28 of the semicircular member 25. The bearing elements 3l may be rotatably supported in the bearing block, if desired', to reduce friction in the relative movement of the parts. The bearing block 29 has a machined opening 3,2 to receive a shaft for the purpose later to be described. Mounted to one side of the semicircular member 25 is a sector gear 33 as by screws` 34, or other well known means, the teeth 35 of which have their center of curvature at the center of the hollow sphere I4.

Within the tubular support I0 is slidably tted a cylindrical block 40 that may be retained therein by screws 4I. The forward end of the block fifil has opposed bores 42 and v43,k and corresponding counter bores 44, 45 and 46, 41. On each of the shoulders formed by the bores 42, 44 and the bores 43, 4B is a exible metal diaphragm 48, 45 having a central contact element 50, 5I. Each counter bore 44, 46 is threaded to receive a threaded cap 52, 53 that securely holds the respective diaphragm in place. The diaphragms are sealed against leakage by corresponding sealing rings 54 and 55 yet each diaphragm is in metal contact with the block 45. Centrally of each cap 52, 53 is an electric installation sleeve 56, '51 threaded therethrough and having a centra-l threaded opening to receive a metal bushing 58, 59, respectively,V the outer end of which is flanged outwardly to secure respectively a terminal plate 50, Giagainst the corresponding insulating sleeve 56, 51. Threaded through each bush-ing; 58, 59 is al contact element 52, 63r that extends outwardly a sufficienty amount to accommodate a closure cap 64I, 65 respectively, threadedv thereon as a locking nut. The outer end of each cap 64, 55 extends through an opening in the tubular support Il flush with the outer surface thereof and has a slot therein to receive a tool, as a screw driver or the like, for the purpose of removing the caps to ,adjust the clearance between contacts 5I), 62 and 5I, 63. Each cap has an opening therethrough communicating with the chamber formed between thel respective cap and diaphragm which, for the purpose of reference, are designated asfchambers a and b, respectively.

In each of these openings isa tube 55, 51 which extend forward for connection to pressure ports, l

later to be described. The innermost chambers, designated as c and d, each has a wall opening through which respective tubes 68, 69 extend for connection to pressure ports to be described.

The block 40 is centrally bored at 15 and counter bored on the back end at 16 and 11. Concentric shafts pass through the'bore 1'5 and the neck portion II of the tubular support I to the forward endV thereof, the outer shaft 18 being supported inv roller type bearings 19 and 80 and having` a pinion gear 8l; fixed to the forward end thereof tel mesh with the sector gear 33. The roller type bearing 'I5`r is supported in the counter bore; 16 of the block 43 while the roller type bearing is supported in a recess in a spider 8:2 formed near the mouth portion I2 of the tubular support IU. Abracket 33 shields the piniony and sector gears 8l, 33 aswell as retains the bearing 30 in place. The inner shaft. 85 is journaled in the bearing block 23, and has a pinion gear 85 on the forward end thereof that meshes with a sector gear 81 which sector gear is integral with a bracket 88 that has bearing portions B9 that are pivotally journaled on the inner wall of the spherical head i4 at diametrically opposed points 90 degrees from the pivotal points 2li, 26 in the same manner and of the same construction as pivots 20, 25. An idler gear 96 is supported on the sector gear 81 and bracket 88 by a bolt SI. Rotation of pinion gear BI imparts'clockwise and counterclockwise rotation (as viewed in Fig. 1)

to the spherical head by the rotation transmitted through the semicircular member 25 on' pivots 20', 26 causing the sphere tol rotate about the pivots 8910i the bracket 88. Rotation of the pinion gear 86 would ,cause rotation of the sphericall headr|4labout the pivotal points 20, 26. It may be seen from the above description that the spherical head |4may be rotated by the two pinion gears 8| and 86 such that the sphere axis of symmetry may be directed throughout a cone mechanically limited-to about 20 degrees of arc from the longitudinal center line of the tubular support.

Corresponding to each axis of rotation of the spherical head I4 are two pairs of pressure ports symmetrically arranged about the sphere axis of symmetry. Pressure ports |00, IUI, which correspond to the axis of sphere rotation vabout the pivotal points 89 and lie in a plane parallel with the plane of the pivotal points 20 and normal to the plane of the pivotal points 89, are connected bythe flexible conduits 69, 66 to the chambers d and b of the switch 5|, 03. The conduits 61, 68 connect the other pair of ports |02, |03, corresponding to the sphere axis of rotation about the pivotal points 20, 26, to the chambers a and c.

The back end of the tubular shaft 18 has a pinion gear ||0 secured thereto. The back end of the pinion gear I I0 is recessed to receive a roller type bearing through which the shaft 85 extends and on which is affixed a pinion gear I I2. Positioned behind-the block 40 in the tubular support I0 isa second block 5 having two eccentric bores ||6 and ||1 and corresponding counterbores ||8 and H9. The counter bore ||8 retains a l roller type bearing |20 while the counter bore ||9 receives a roller type bearing |2I. Through the bore IIB and bearing |20 is a shaft |22 having the forward end reduced to receive and retain a pinion gear |23 that is in mesh with the pinion gear H2. A shaft |24 extends through the bore ||1 and the roller bearing |2| and has the forward end reduced to receive and retain a pinion gear |25 that is in mesh with the pinion gear ||0. Connected to each shaft |22 and |24 is a reversible type drive motor |26, |21, respectively, connected by any suitable coupling means. Rotation of the motor |21 produces rotation of the spherical head I4 about the pivots 89, hereinafter referred to as the pitchv axis, through the shaft |24, gears |25, 0, shaft 18, pinion and sector gears 8|, 33 and semicircular ring 25; while rotation of the motor |26 produces rotation of the spherical head |4 about the pivots 26, hereinafter referred to as the yaw axis, through the shaft |22, gears 23, H2, shaft 85, gears 86, 81 and bracket 88.

In order to limit the relative movement of the spherical head about either of its axes of rotation and to avoid damage to the device, limit switches are associated with the mechanical couplings of the drive motors to interrupt the motor circuit just prior to the spherical head reaching its mechanical limit of rotation. While the placement of these limit switches is of little importance, it appears expedient to -associate these switches with the shafts directly connected to the motors. On each of the shafts |22, |24 are cam member |30, |3| respectively, that are welded or otherwise securely fastened to the respective shaft. Fora. better understanding of the arrangement of the cam member and the limit switches, reference is made to Fig. 3 wherein for the purpose 'i switch actuating arms |33'and |34 of a normally open switch |35 and a normally closed switch |36, respectively.

A better understanding will be had of the circuit arrangement of cach control motor by reference to Fig. 4 wherein a circuit for only one drive motor is shown in that the circuit for each drive motor is the same. Using the drive motor I 21 for the purpose of explanation, this drive motor is represented electrically by the same reference character and as having a field winding |40 for clockwise rotation of the motor, looking forwardly over the motor as illustrated in Fig. 1, and a field winding lill for counterclockwise rotation. rIhe field windings join, as is conventional with this type motor, into conductor |42 connected to a voltage source. Field winding |40 is connected through conductor |43 to one arm |44 of a two-blade relay switch, generally referred to by the reference character |45. The other end of the field winding IQI is connected by conductor |06 to the other switch arm |41 of the relay switch |45. The stationary poles of the relay switch |45 are both connected to ground through conductors |40 and |40 respectively, the relay contact arms being biased such that the contact arm |44 is normally closed through the conductor |48 to ground and the contact arm |41 is normally open. The two contact arms |44 and |41 have an armature associated therewith and represented in dotted lines which is influenced by a solenoid coil |50 upon energization to connect arms |01 to contact |49 and break the connection between |44 and |48. One end of the solenoid coil I 50 is connected by conductor |5| to a voltage source and the other end is connected through conductor |52 to one pole each of the limit switches |35 and |35. The stationary contact of the limit switch |35 is connected to ground while the stationary contact of the limit switch |36 is connected by conductor |53 to the terminal 6| of contact element 03, the contact 5I on the diaphragm 48 being grounded.

Referring again to Fig. 1, each motor |26, |21 has a rearwardly extending portion of the rotor shaft that is each, respectively, connected to a self synchronous motor transmitter |10, |1| by a coupling |12, |13. These couplings may be of any of the well known types to couple the shafts of the respective drive motor with the self synchonous transmitter motor and is shown merely as a coupling sleeve for securing these shafts. The self synchronous transmitter |10 is electrically coupled to a self synchronous receiver motor |14 by the cable |15, the synchronous receiver shaft being mechanically connected to the indieating hand of a pitch angle indicator |16 to register pitch angles of the aircraft on which the device is used in accordance with the pitch deviation of the aircraft with respect to the air stream. The self synchronous transmitter |1| is electrically coupled by the cable |11 to a self synchronous receiver motor |10 which operates a yaw indicator |19. The rotor windings of the self synchronous transmitters and receivers are supplied by a voltage source as is well known in the art to produce signal intelligence in the system.

For the purpose of assembling the device on a vehicle as an airplane, referring to Fig. 5, a ange |60 that conforms to the surface to which it is to be attached may be riveted or welded to the tubular support I0. To expedite assembly, the tubular support I0 may be divided at |6| and the rearmost section of the tubular support I0. re-

7 tained on the block 40' by screws in the same manner as the. foremost section. It should also be further understood that the spherical head I4 is retained on the spherical seat I3 on the tubular support I by reason of the central shaft 85 having the pinion gear 85 bear against the bearing block 29 and the block bear againstv the semicircular member 21 holding the spherical head rearwardly since the shaft 85 is retained against any forward longitudinal movement by the pinion i gear I|2 bearing against the roller bearing III.

Where desirable, a sealing ring may be arranged in the spherical seat I3 to seal out dirt and moisture, The spherical head member |4 may be easily and quickly removedfrom the assembly by loosening one of the Vset screws I1 that seat in the semi-circular ring sockets 26. The gears 86,

|31v and 90 will separate without difliculty. The fluid conduits 66-69 may have couplings as rubber sleeves to facilitate attachment and detachment.

In the explanation of the operation of the device,V let it be assumed for the purpose of illustration that the device is installed on aircraft to indicate pitch and yaw angles. The tubular support is preferably mounted by the flange |60 on the leading edge of an aircraft airfoil, nacelle,

` or fuselage such that the longitudinal centerline of the tubular support is parallel to the longitudinal centerline of the aircraft and the spherical head is in the free airstream. The pitch and yaw indicators |16 and |19 together with their respective synchronous receiver motors are installed on the instrument panel of the aircraft as is conventional., When the sensing head axis of symmetry is aligned with the longitudinal centerline of the aircraft, the pitch and yaw indicators will read zero as illustrated in Fig. 1. Asthe aircraft takes off the runway, the pitch and yaw device is turned on for operation. The circuit is immediately established to cause motor |21 to rotate clockwise to effect counterclockwise rotation of the sensing head I4. The pressure in the sphere head port |00 becomes greater than the pressure in port due to the inclination of the aircraft for take-off which will close contacts 5|, 63 placing the relay coil |50 in a closed circuit to switch the contact arms |44 and |41 to the lower position and causing rotation of the turn motor |21 in the counterclockwise direction, looking in the forward direction of the device, which will cause rotation of the spherical head clockwise until the pressure in ports |00 andv |0I are equal whereupon the circuit through the relay coil is broken at 5|, 63. The circuit will then be completed through the reversing motor field winding |40 to cause counterclockwise rotation of the spherical head I4. In actual practice, one of the field windings |40 or |4I are constantly energized to cause oscillation of the spherical head I4V about its pitch axis to maintain equal pressures in the ports |00 and |0I. This oscillation, however, is extremely slight--so slight in actual practice that the movement of the spherical head is not perceptible to the eye or to the touch. This oscillation can be increased by withdrawing the contact 63- fromk the contact 5| but the greater precision is reached flowing airstream. The greater the spherical head I4 must be rotated clockwise to provide direction of the turn motor.

equal pressure in the ports |00y andY IUI, the; greater will be the upward'v registration in degrees on the pitch indicator |16. It mayr be readily seen that downward. pitch angles may be indicatedV asreadily as upward pitch angles4 by the device.

The useful range of pitch angles is from zero to about 15` degrees and: therefore. the instrument is built to cover a 20 degree range which would provide ample pitch. anglesv for. all

conditions for flying. If for any reason' the spherical head I4- is drivenv to approach one of its limits of rotation, the cam node |32 will operate one of the limit switches to reverse the. For' example, in4 the event the spherical4 head |41 is being rotatedclockwise approaching its mechanical limit, as viewedin Fig. 1, the switch |36 will be opened (see Fig. 3) and the relay |45 cle-energized to. connect the field winding |40v to'A rotate thek drive motor and shaft |24' clockwise and the shaft 18 and spherical head I4 counterclockwise until. the cam node |32 permits the switch |36` to again make contact. The turn motor will oscillate to make and break theV contacts of limit switch |30. as long as the unusual pitch angle condition exists.

Control of the spherical. head I4 about itsyaw axis, or pivots 20,v 25, is carried out in the same manner as described' for the pitch control. Any unequal pressures in the ports |02', |03', are transmitted through the uid conduits; 61,. 68 to'opposite sides of the diaphragm 48 wherein the contacts 50, 62 are conditioned to make 0r break.

the circuit` in the coil of relay |45 which' relay controls the direction of the drive motor |25 to rotate the spherical head I4 to'nu-ll or equalize the pressure in ports |02, |03. The self synchronous transmitter-receiver system I1I, |18'r isA effective to transmit the angular position rightr or left of the` sphere axisv of symmetry with re,- spect tothe longitudinal centerline of the' tubular' support through the control shafts and thusregister on the yaw indicator |19 the position: of the longitudinal. reference li-nefof the( aircraft with respect to the relative airstream. The anguiar deviation in either the' right orv left direc:- tion is limited by limit switches in a maximum of 20 degrees in the same manner as the: pitch angulation is limited. While mechanical. relays |45 and |45 are shown andY described for thev circuit, it is to be understoodv that electronic relays may be used, andv in actual practice are used, to provide superior control and reduce hunting in the system. For thel purposev of illustration the sensing head member I4 is shown and described as being spherical, which provides good aerodynamic results for subsonic speeds', but the sensing headmay take other forms to'v adapt the device for use atVV transonic and super-- sonic speeds.

It is believed to be further understood that both of these pitch and'v yaw operations takeY place` simultaneously such that simultaneous registration of both the pitch and yaw angles are available' to the aircraft flight personnel; The two indicators may be made as oneinstru-ment, where desirable cr feasible, such that both indications'- maybe-readfro'rn asingle dial.

From the foregoing rit may be understood that various changes and modifications may bemade in the structure and details without departing from the spirit and scope of' this invention and I desire to be limited only by the scope of the appended' claims.

1l.. A'universallymounted sensingl headfor null Apressure?typepitch and'yaw indicating devices comprising; a tubular boom having a spherically concave open end; two concentric shafts consistl" said sensing head on an axis perpendicular to n an axis of symmetry of -said sensing head, said semicircular ring member being divided at its mid portion through which divided portion said solidshaft extends, a bearing member retained between the inner radial surface of said semicircular ring member and said pinion of the solid shaft, and said semicircular ring member having a sector gear in mesh with the pinion gear of said tubular shaft; a bracket having its ends journaled to the inner wall of said sensing head on an axis perpendicular to said axis of symmetry and the axis formed by the journals of said semicircular ring member and having a sector gear thereon in mesh with said pinion gear of said solid shaft; means providing two pairs of pressure ports arranged in said sensing head on the side remote from the concave open end of said boom and being symmetrically positioned about said axis of symmetry in planes corresponding to the two sensing head axes of rotation, a pair of pressure responsive motor controlling devices in pressure communication respectively with said two pairs of pressure ports, a pair of drive motors connected respectively to said tubular shaft and said solid shaft and each responsive to one of said pairs of pressure responsive motor controlling devices to maintain the corresponding pairs of pressure ports in equal pressure relation through said concentric shafts and whereby rotation of said tubular shaft rotates said sensing head about its axis formed by the bracket journals and rotation of said solid shaft rotates said sensing head about its axis formed by the semicircular ring member journals to provide angular sense of said sensing head axis of symmetry with respect to the airstream in both the vertical and horizontal planes.

2. In a differential pressure null type pitch and yaw control device having a universally mounted sensing head sensitive to flow characteristics in the vertical and horizontal planes comprising; a hollow truncated spherical sensing head with an opening into said sensing head at the truncated plane, said head having two sets of ports in normally arranged planes symmetrical about an axis of symmetry of said sensing head and in the hemisphere removed from the truncated hemisphere; two brackets having the ends thereof journaled to the inner surface of said sensing head, each being journaled along a diameter of said sensing head in a plane of each of the corresponding sets of ports, the plane through the journals of both said brackets being normal to the sensing head axis of symmetry, and each bracket having a sector gear thereon and centrally thereof rotatable in a plane parallel with the plane passing through the journals of the corresponding-bracket and 'the plane of the axis of symmetry; a boom adaptable to be mounted in'4 an air ow region and having a spherically concave open end receiving the truncated hemisphere of said sensing head in a manner that said sensing head opening is directed into said boom; means for retaining said sensing head against the concave surface of said boom to permit limited universal rotative movement of said sensing head with respect to said boom; two pressure responsive drive motor controlling means in said' boom each in fluid communication with one each of said sets of ports; two drive motor shafts journaled in said boom, each having a pinion gear thereon in mesh with one each of said bracket sector gears whereby rotation of one of the drive `motor shafts produces rotation of said sensing vhead about a diametrical axis effected'by the journals 'o'f one of said lbrackets and rotation of `said other 'drive motor shaftimparts rotation of ythe sensinghead about a diametrical axis effected by-the 'journals of the other of said brackets, simultaneous rotation of said drive motor'shafts producing universal rotary -movement of `said sensinghead, and twodrive motors connectedv respectively to said two drive motor shafts and being responsive for operation to said two pressure responsive drive motor controlling means. l

3. In a differential pressure null type pitch and yaw control device as set forth in claim 2 wherein said two sets of ports constitute two pairs and the fluid communication between corresponding pairs of ports and pressure responsive drive motor controlling means is effected through flexible tubing.

4. In a differential pressure null type pitch and yaw control device as set forth in claim 2 wherein said means for retaining said sensing head on said boom is effected by one of said brackets being semicircular and divided in the central portion thereof through which divided portion one of the drive motor shafts extends and is retained from separation by the pinion gear of said last mentioned drive motor shaft.

5. In a differential pressure null type pitch and yaw control device as set forth in claim 4 wherein said two drive motor shafts are concentric shafts consisting of an inner shaft and an outer tubular shaft the inner shaft of which extends through the divided portion of said semicircular bracket.

6. A differential pressure null type pitch and yaw indicating device comprising; a support for attachment to a mobile vehicle in free airstream relation, a hollow sensing head, means for universally mounting said sensing head on said support including two bracket members having the ends thereof pivoted to the inside surface of said sensing head in a plane normal to an axis of symmetry of said sensing head with the pivots of one bracket being separated by a right angle from the pivots of the other bracket to provide two normally arranged axes of rotation for said sensing head, one of said axes constituting a pitch axis and the other constituting a yaw axis, rotatable bearing means on said support to slidably engage a portion of one bracket for rotatable and rockable support thereof on said support about a point at the intersection of said normally arranged axes, means providing two sets of pressure sensing ports on said sensing head in normally arranged planes and symmetrical about an axis of symmetry of said sensing head, two differential pressure responsive control means having pressure communication with the respec- 11 tive sets of ports, and two independently Operable means lresponsive to said .two .control Ameans respectively to actuate said two bracket vmembers and .thereby .exercise rnull position control over .said sensing head in response to the pressures at :the ports of said two sets thereof.

7; A differential pressure null type pitch `and yaw indicating l,device as set `forth in claim 6 wherein said `one bracket rotatable andvrockable on said .support is semicircular and has the central portion thereof divided, and wherein said rotatable bearing means comprises a bearing block received in said :divided central portion and engaging vrthe inner radialsurface of said semicircular bracket which bearing block is Withheld against separation `from said support, and the other Abracket is disposed substantially Within the semieircular bracket whereby `rotation of the lsemicircular 'bracket .about its center imparts rotation of said sensing head .about one of its axes of rotation and rotation of said other bracket about a point intermediate its journals with said sensing head imparts rotation of said sensing head about the other of `its axes of rotation.

`8. A differential :pressure null type pitch and @12 yaw indicating device as set forth 'in Iclaim 7 wherein the bearing block is withheld yfrom sepa-y ration from said support by a drive motor shaft having la pinion gea-r on its 4outer endabutting said :bearing block, said ydrive motor Ashaftv ypinion 'gear being in mesh Ywith `a sector gear on said other bracketwherebyerotation-of -said drive motor shaft imparts rotation to said sensing head through said other bracket, and a tubular shaft concentric with said first 'mentioned shaft :and having ,a pinion gear thereon in mesh vwith a sector gear Aon said semicircular bracket whereby rotation of 4said tubular shaft produces vrotation vfile of this patent:

' UNITED STATES PATENTS Name Date Young Man 8, .1949

Nurriber 

